mm/vmalloc: add support for __GFP_NOFAIL

Dave Chinner has mentioned that some of the xfs code would benefit from
kvmalloc support for __GFP_NOFAIL because they have allocations that
cannot fail and they do not fit into a single page.

The larg part of the vmalloc implementation already complies with the
given gfp flags so there is no work for those to be done. The area
and page table allocations are an exception to that. Implement a retry
loop for those.

Signed-off-by: Michal Hocko <mhocko@suse.com>

mm/vmalloc.c

@@ -2941,8 +2941,10 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	else if (!(gfp_mask & (__GFP_FS | __GFP_IO)))
 		flags = memalloc_noio_save();
 
-	ret = vmap_pages_range(addr, addr + size, prot, area->pages,
+	do {
+		ret = vmap_pages_range(addr, addr + size, prot, area->pages,
 			page_shift);
+	} while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
 
 	if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
 		memalloc_nofs_restore(flags);
@@ -3032,6 +3034,8 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		warn_alloc(gfp_mask, NULL,
 			"vmalloc error: size %lu, vm_struct allocation failed",
 			real_size);
+		if (gfp_mask && __GFP_NOFAIL)
+			goto again;
 		goto fail;
 	}